Patrick Ness’ A Monster Calls, like the best stories for children, is wild. It’s ambiguous, in the slightly threatening sense of the word. It isn’t easy. Sally Cookson’s new adaptation of the book at the Old Vic retains all the deep-rooted complexity of Ness’ work and, what’s more, conveys its poetry. This is, after all, the story of what happens when a monster “comes walking”, the very phrase suggesting the scale: that something very old and strange is happening.

The boy at the centre of the story is Connor, played by Matthew Tennyson. No-one in Connor’s life is telling him what he wants to hear. His Mum is seriously sick, his Grandma worried and clashing with Connor, his Dad only able to spare limited time away from his other, new family in America. Connor’s struggling with bullies at school, increasingly frustrated at his ineffectualness, and he keeps waking up at 12:07 each night to a monster who wants Connor to listen to his tales. And time seems to be running out.

Marianne Oldham and Selina Cadell are heartbreaking as Connor’s Mum and Grandma, in a play which asks a lot of them with the utmost concision. You can see the exhaustion in both characters, though Connor tries desperately not to. John Leader is another standout as the school bully Harry, holding the lapels of his jacket stiffly, like a king. As Connor, Tennyson has one of the most RP accents I’ve ever heard; his performance is absolutely focused and vulnerable, but none of the three kids who bully him at school speak like him, a slightly jarring choice.

The ensemble’s devising process with Cookson, Dan Canham (movement), Matt Costain (aerial) and Laura Cubitt (puppetry) together makes for an entirely distinctive and smooth play: manipulating the ropes hanging from the flies to create the monster, a car, to suspend an actor, the ensemble are always present, an intent part of everything that’s happening. At times, they visibly operate pulley systems with the weight of their own bodies, climbing and dropping to manipulate the action or twisting in the air, using the ropes like aerial silks. In one effortless moment, the ensemble sat at either side of the stage hear the monster at real, menacing volume for the first time and slide sickeningly from their chairs as if melted at his voice: they are subsumed to become him a moment later.

The representation of the monster – a green man, a dryad of sorts, the colossal manifestation of the yew tree on the hill visible from Connor’s house – is a theatrical feat. While I don’t think the full effect of Jim Kay’s illustrations is quite achieved, it would be hard to represent that power and strength, the thickness of the trunk and the dark mass. The company wraps, ties, entangles themselves in the ropes with Stuart Goodwin as the voice and “face” to the monster, sometimes aloft, higher than the rest, and sometimes just walking around Connor: he doesn’t need to be attached to his rope-body at all times for us to see who he is, with his simple yew berry necklace. This network of ropes casts perfect shadows for the sinister, reaching branches, all the tales of the yew tree-monster a physical part of him, and increasingly the events in Connor’s life, too. Despite lacking the hellish, crowded shading Kay’s illustrations had, the design here is awe-inspiring, topped off by the effects on Goodwin’s voice making him sound like a wolfish Ent.

The music stuns. A live score by Benji Bower and Mike Beer using cello, drum machine, synths, and piano transforms endlessly alongside and above the action: we see the musicians through a panel in the white backdrop which largely conceals them when the monster’s present. Autotuned vocals reminiscent of James Blake underscore that wildness; barring a dud of a song during the second tale (sung skilfully by Nandi Bhebhe but with clunking lyrics that should have just been left as speech), the score should be made available for everyone, and they should hear it.

The Old Vic warns on its site that this play isn’t for young children, but there were still some I’d say were too young in my audience. A Monster Calls is difficult and painful, abstract and still clear for children to grasp what’s going on without trouble, but it might involve some thorough consoling work on the part of parents. Adults around me were sobbing by the end. Above all, though, it’s beautiful – the actors stand starkly in the harsh flash of lights against that background, like thick white paper ripe for drawing on.

Siobhan Dowd’s idea, realised by Ness, has again been honoured in a deserving way; she died of cancer before she could write the story herself, and he and Kay constructed it together after her death. As Ness noted about his book, it was true to her while also undeniably diverging from what she’d envisioned: and here again it has been set free, allowed to grow and change. Wild.

A Monster Calls is on at Old Vic Theatre until 25th August. More info here.

Frey Kwa Hawking works as a dramaturg in London. He likes to go to the theatre and the cinema. Sometimes they let him in. He is trans and Malaysian-Chinese. He always orders xiao long bao. Follow him on Instagram and Twitter @absentobject